In the LED lighting apparatus for lighting by connecting two or more. LEDs in series with a constant current source, arc discharge occurs in a circuit by open mode failures, such as detachment of each terminal portion, loose connection, disconnection in the circuit and opening of bonding wires of the LEDs. When the arc discharge is detected by rise of an output voltage of the constant current source, it has been known to provide a control unit to stop the supply of direct current.
In an arc discharge characteristics between electric contacts, it is known that a minimum arc voltage Vm and minimum arc current Im almost agree with a voltage value 13V, and a current value 0.43 A of Holm, respectively in case copper is used, as material of the contacts.
Inventors found out that the arc discharge is suppressed at the time of open mode failures of a load circuit under condition in which a voltage difference between a maximum output voltage of a DC power supply source and a load voltage at the time of normal operation is less than 20V as a result of their investigation, and research.